A BIOMETRIC STUDY OF THE CONIDIA OF 

 MACROSPORIUM AND ALTERNARIA. 



By F. W. Wakefield, 

 District Forester, Southern Tasmania. 



(Witli 1 Text Figure;.) 



(Read 10th April, 1922.) 



Alternaria and Macrosporiurn are closely allied genera 

 of the Hyphomyctacex, both being included in the section 

 Dictyosporx of the Dematicse. They are differentiated by 

 their methods of conidia-formation. In Macrosporiurn a 

 conidiophore bears at its apex a single conidium, which at- 

 tains its full size, matures, and finally becomes detached. In 

 the case of Alternaria, the conidiophore produces at its apex 

 a chain of conidia, each of which is morphologically identical 

 with the single conidium of Macrosporiurn. This chain of 

 conidia produced by Alternaria eventually becomes broken 

 up into individuals which cannot be distinguished from a de- 

 tached conidium of Macrosporimn. It is, therefore, only 

 possible to refer a particular species to one or other of 

 these two genera when the manner in which the conidia 

 are produced has been determined. Consequently, many 

 species have been incorrectly placed, owing to inaccurate 

 observations on the conidia and method of conidia-forma- 

 tion. 



The abundance of species apparently placed indis- 

 criminately in either genus and having synonyms in the 

 complementary genus is evidence of the fact that these two 

 genera are much confused. Thus Alternaria solavi, 

 SoTauer= Macrosporiurn solani, E. & M. 



The ease with which the concatenate conidia of 

 Alternaria become fragmented into free individuals when 

 mounted in water for miscroscopical examination explains 

 the frequency of inaccuracies in classification. It will be 

 seen that when a species of either genus is mounted in water 

 the resulting "object" is the same, i.e., there will be similar 

 conidiophores and morphologically identical conidia. It 

 will be shown later, however, that these latter may be 



